I was thinking about doing more random seed runs, just wanted to know if you forgot to do /seed after a run in 1.16 if it could still get accepted

yes im pretty sure ive seen @realbenex do it

I think you can get away with it provided nothing else is sus. Although the best idea would be to just remember to do it

You don't need to do /seed after the run, but you need to provide the seed, or else your run will be rejected.

If it's an honest mistake then it's like fine on a first offense, but also note that as @Solicial said it doesn't matter whether you do /seed in the video as long as the seed is provided